Nuisance Fault Elimination: Commissioning Guide

By Dovydas Kersys · Chapter 49 of 58 in Machine Commissioning.

Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.

Nuisance faults are real faults whose thresholds, timing, signal quality or logic make them occur when the machine is actually acceptable. Commissioning should reduce nuisance alarms without masking genuine problems.

Why this matters during commissioning

Operators quickly learn to ignore alarms that trigger unnecessarily. That destroys the value of the alarm system.

Commissioning procedure

Collect fault timestamps and operating conditions.
Identify whether the source is signal chatter, timing margin, mechanical variation, network delay or bad logic.
Measure the real signal/event before changing debounce or timeout values.
Make the smallest justified change.
Retest the fault condition and the normal condition.

Common failure patterns

Increasing every timeout instead of fixing a slow actuator.
Adding debounce to hide an intermittent connector.
Disabling an alarm instead of correcting its source.
Using a timer to replace missing positive feedback.

Evidence to record

Measured value and test point
Expected value / expected state
Observed value / observed state
Pass/fail result and any deviation
Name/date or responsible person where required

FIELD RULE: Never tune away a fault until you understand what the original signal was doing.

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